Optical element manufacturing method

ABSTRACT

An optical element manufacturing method includes a first process for forming a mask pattern on a substrate, and a second process for forming a step-like structure on the substrate by use of the mask pattern, wherein the first and second processes are repeated N times, and wherein, before execution of the (k)th time second process where 2≦k≦N, there is a process for determining a relative alignment error between a mask pattern as formed through the (k)th time first process and a mask pattern as formed through the (k-1)th time first process, and wherein the height of the step-like structure to be defined by the (k)th time second process is determined in accordance with the alignment error.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to an optical element manufacturing method and,more particularly, to a method of manufacturing a binary typediffractive optical element.

Many types of optical systems with a diffractive optical element usinglight diffraction phenomenon have been proposed. As examples of suchdiffractive optical elements, there are a Fresnel zone plate, adiffraction grating and a hologram.

Generally, for a diffraction type optical element having a blazed shape,the manufacture becomes more difficult with the decrease in pitch. Asregards the shape of the diffractive optical element, if a shape ofbinary type is selected, semiconductor device manufacturing techniquescan be applied to the manufacture of it, and a fine pitch can beaccomplished relatively easily. For these reasons, research anddevelopments have recently been made on binary type diffractive opticalelements wherein the blazed shape is approximated by use of a step-like(with levels) shape.

For details of a binary type diffractive optical element, reference maybe made to the following publications:

a) G. J. Swanson, "Binary Optics Technology: The Theory and Design ofMulti-level Diffractive Optical Elements", Massachusetts Institute ofTechnology Lincoln Laboratory, Technical Report 854, Aug. 14, 1998.

b) G. J. Swanson, "Binary Optics Technology: Theoretical Limits on theDiffraction Efficiency of Multilevel Diffractive Optical Elements",Massachusetts Institute of Technology Lincoln Laboratory, TechnicalReport 914, Mar. 1, 1991.

Referring to FIG. 5 showing the manner of manufacturing an opticalelement according to the present invention, the manner of manufacturinga binary type diffractive optical element of four-level structure willbe briefly explained.

Denoted in the drawing at 100 is a transparent glass plate of arefractivity n, and denoted at 101 is a resist. Denoted at 102 is a maskto be used for a first exposure. Denoted at 103 is exposure light. Inthis example, the resist 101 comprises a positive type resist.

First, in process A, a pattern of a mask 102 is transferred to theresist 101 by use of the exposure light 103. In process B, developmentof the resist 101 is performed. In process C, etching of the glasssubstrate 100 is performed while the resist 101 after being developed isused as a mask pattern. Then, in process D, unnecessary resist on thesubstrate 100 is removed, whereby a binary type optical element oftwo-level step structure is accomplished.

The etching depth d₁ in process C is determined, when the wavelength tobe used with the binary type optical element is λ, by the followingequation:

    d.sub.1 =λ/[2(n-1)]

Subsequently, to the glass substrate 100 on which a binary type opticalelement of two-level structure has been formed, a resist material (104 )is applied again, and in process E a mask 105 is used to perform asecond exposure. The pattern of the mask 105 has a pitch a half of thepattern of the mask 102. The exposure is performed while correctlyaligning the edge of a light blocking portion of the mask 105 patternwith the edge of the two-level binary structure. By these procedures andafter the development treatment at process F, a resist pattern asillustrated is formed.

Subsequently, in process G, second etching is performed by using theresist pattern formed in process F as a mask pattern. In process H,unnecessary resist is removed, whereby a binary type optical element offour-level structure is accomplished. Here, the etching depth d₂ inprocess G is determined by the following equation:

    d.sub.2 =λ/[4(n-1)]

While the foregoing description has been made in relation to afour-level structure, as is well known in the art, a binary type opticalelement of eight-level structure or sixteen-level structure can bemanufactured by repeating the above-described procedure while changingthe mask pitch.

In process E of the processes for manufacturing a binary typediffractive optical element described above, it is not easy to align themask 105 for the second exposure with respect to the mask 102 of thefirst exposure. Usually, there occurs a registration error (alignmenterror) of some degree.

The effect of such alignment error will be described with reference toFIGS. 1A, 1B, 2A and 2B. Denoted in the drawings at 110 is a glasssubstrate on which a diffraction grating of two-level structure has beenformed. Denoted at 111 is a mask for use in second exposure.

Here, one period of the two-level structure is T, and the mask 111 has alight blocking portion of a width T/4. Denoted at 112 is a coordinateaxis for explanation, and the pattern formed on the glass substrate 110has a periodicity in X-axis direction.

FIG. 1A shows a state in which the mask 111 is deviated from anidealistic position, in positive X-axis direction by aT/4 (a>0).

If processes E-H in FIG. 5 are performed in this state, then anaccomplished diffractive optical element will have a shape such as shownin FIG. 1B.

FIG. 2A shows a state in which the mask 111 is deviated from anidealistic position, in negative X-axis direction by |aT/4| (a<0). Ifprocesses E-H in FIG. 5 are performed in this state, then anaccomplished element will have a shape such as shown in FIG. 2B.

With these shapes, as a matter of course, there occurs a decrease ofdiffraction efficiency. When the diffraction efficiency of first-orderdiffraction light is calculated by using the value "an" as a parameter,it follows that:

    |C.sub.1 |.sup.2 =(8/π.sup.2){1-sin[π(|a|/2]}      (1)

Equation (1) is derived in accordance with scalar theory, and details ofit will be described later with reference to embodiments of the presentinvention. The result can be shown in a graph, such as that of FIG. 3.In the case where there is no alignment error, that is, when a=0, anidealistic diffraction efficiency of 81% is attainable with respect tothe four-level structure. However, with enlargement of alignment error,the diffraction efficiency decreases considerably. Since the decrease ofdiffraction efficiency leads to various problems such as a decrease ofusable light quantity or an increase of unnecessary diffraction light,causing flare or the like, it should be suppressed as much as possible.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an optical elementmanufacturing method in which an alignment error, if any, may causesmall reduction of diffraction efficiency.

In accordance with an aspect of the present invention, there is providedan optical element manufacturing method, comprising: a first process forforming a mask pattern on a substrate; and a second process for forminga step-like structure on the substrate by use of the mask pattern;wherein the first and second processes are repeated N times, andwherein, before execution of the (k)th time second process where 2≦k≦N,there is a process for determining a relative alignment error between amask pattern as formed through the (k)th time first process and a maskpattern as formed through the (k-1)th time first process; and whereinthe height of the step-like structure to be defined by the (k)th timesecond process is determined in accordance with the alignment error.

In accordance with another aspect of the present invention, there isprovided an optical element manufacturing method, comprising: a firstprocess for forming a first mask pattern on a substrate; a secondprocess for forming a step-like structure on the substrate by use of thefirst mask pattern; a third process for forming a second mask pattern onthe substrate; a fourth process for determining a relative alignmenterror between the first and second mask patterns; and a fifth processfor forming a step-like structure on the substrate by use of the secondmask pattern, wherein the height of the step-like structure to be formedthrough the fifth process is determined in accordance with the alignmenterror.

In accordance with a further aspect of the present invention, there isprovided an optical element manufacturing method, comprising: a firstprocess for forming a mask pattern on a substrate; a second process fordetermining a relative alignment error between a mask pattern justhaving been formed and a mask pattern previously formed; and a thirdprocess for forming a step-like structure on the substrate by use of themask pattern just having been formed, wherein the height of thestep-like structure to be formed through the third process is determinedin accordance with the alignment error.

The present invention can be applied to an optical element manufacturingsystem, or to an illumination system or exposure apparatus having anoptical element manufactured in accordance with the optical elementmanufacturing method. Also, the invention can be applied to a devicemanufacturing method which uses such an exposure apparatus.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views, respectively, for explaining therelation between alignment error and the shape of optical element.

FIGS. 2A and 2B are schematic views, respectively, for explaininganother example of the relation between alignment error and the shape ofoptical element.

FIG. 3 is a graph for explaining the result of calculation on alignmenterror and diffraction efficiency.

FIG. 4 is a flow chart for explaining the procedure of manufacture of abinary type diffractive optical element according to an embodiment ofthe present invention.

FIG. 5 is a flow chart for explaining the procedure of manufacture of abinary type diffractive optical element of four-level structure,according to an embodiment of the present invention.

FIG. 6 is a schematic view for explaining the relation between alignmenterror and phase distribution of optical element.

FIG. 7 is a schematic view for explaining another example of therelation between alignment error and phase distribution of opticalelement.

FIG. 8 is a graph for explaining the result of calculation on etchingdepth and diffraction efficiency.

FIGS. 9A and 9B are schematic views, respectively, for explainingexamples of mask pattern.

FIG. 10 is a schematic view for explaining positional relationshipbetween images of two alignment error measurement marks.

FIGS. 11A and 11B are schematic views, respectively, of a main portionof an illumination system into which an optical element manufactured inaccordance with an embodiment of the present invention is incorporated.

FIGS. 12A and 12C and FIGS. 12B and 12D are enlarged schematic views ofa diffractive optical element in the structure shown in FIGS. 11A and11B, respectively.

FIG. 13 is a schematic view of a main portion of a projection exposureapparatus into which an optical element manufactured in accordance withan embodiment of the present invention is incorporated.

FIG. 14 is a flow chart for explaining device manufacturing processes.

FIG. 15 is a flow chart for explaining details of a wafer process in theprocedure of FIG. 14.

FIG. 16 is a schematic view of a manufacturing system based on amanufacturing method according to an embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4 is a flow chart of optical element manufacturing method,according to an embodiment of the present invention. FIG. 5 is aschematic view for explaining the procedure of manufacture of an opticalelement in this embodiment of the present invention, for manufacturing abinary type diffractive optical element of four-level (four-step)structure.

Denoted in FIG. 5 at 100 is a transparent glass substrate of arefractivity n, and denoted at 101 and 104 are resist materials. In thisexample, each of the resists 101 and 104 comprises a positive typeresist. Denoted at 102 is a mask (first mask) to be used for a firstexposure, and denoted at 105 is a mask (second mask) to be used for asecond exposure. Denoted at 103 or 106 is exposure light.

First, in process A, a pattern of the first mask 102 is transferred tothe resist 101 by use of the exposure light 103. In process B,development of the resist 101 is performed. In process C, etching of theglass substrate 100 is performed while the resist pattern defined by thedevelopment is used as a mask pattern. Then, in process D, unnecessaryresist on the substrate 100 is removed, whereby a binary type opticalelement of two-level step structure is accomplished.

The etching depth d₁ in process C is determined, when the wavelength tobe used with the binary type optical element is λ, by the followingequation:

    d.sub.1 =λ/[2(n-1)]

Subsequently, to the glass substrate 100 on which a binary type opticalelement of two-level structure has been formed, a resist material (104)is applied again, and in process E the second mask 105 is used toperform a second exposure.

In this embodiment, the pattern of the mask 105 has a pitch a half ofthe pattern of the mask 102. In process E, the exposure is performedwhile correctly aligning the edge of a light blocking portion of themask pattern with the edge of the two-level binary structure. In processF, development treatment is performed whereby a resist pattern asillustrated is formed.

Process E has been explained above with respect to an example whereinthe pattern of the mask 105 and the pattern of the mask 102 arecorrectly aligned with each other. Practically, however, it is not easyto align the mask 105 with the mask 102, more exactly, to align the mask105 with the substrate 100 on which a two-level step-like structure hasbeen formed by use of the mask 102. In practice, there occurs aregistration error (alignment error) between these masks.

In this embodiment, in consideration of the above, after completion ofthe exposure (process E) using the second mask 105 and the development(process F), measurement of alignment error is performed. Then, on thebasis of the measured alignment error, an optimum etching amount iscalculated, as will be described later, and, in accordance with thecalculation, the etching is performed in subsequent process G.

Then, in process H, unnecessary resist is removed whereby a binary typediffractive optical element of four-level structure is accomplished.

Now, the manner of determining the etching amount in accordance with theamount of alignment error between the second mask 105 and the first mask102, in process E, in the present embodiment will be explained.

The relation between the alignment error of the second mask 105 and thediffraction efficiency of first-order diffraction light is such as shownin FIG. 3. Here, calculation of diffraction efficiency is performedagain, while taking into account the relation with the etching depth inthe second etching process. According to the scalar theory, thediffraction efficiency of (m)th-order diffraction light from a structurewhich has a period T in X direction and which provides a phasedistribution p(x) with respect to incident plane wave front, can becalculated by using a square of an absolute value of ##EQU1## that is,by using |C_(m) |².

First, the shape shown in FIG. 1B where a>0 may be expressed in terms ofa phase function. In this case, the depth d₁ of first time etching iskept at

    d.sub.1 =λ/[2(n-1)]

that is, it is kept fixed at the phase difference π. However, the depthd₂ of the second time etching is set as

    d.sub.2 =[λ(1+b)]/[4(n-1)]

and the phase difference is expressed as (1+b)π/n. This makes itpossible to take into account the effect of the second time etchingdepth d₂ upon the diffraction efficiency, using b as a parameter.

It is seen from the above that the phase function p(x) may be determinedas illustrated in FIG. 6. While the origin of phase may be set asdesired, here, for convenience, it is set as shown in FIG. 6.Calculation may be made while taking the X-direction range from 0 to Tas one period and, in regard to first-order diffraction light, fromequation, the following equation may be derived. ##EQU2## Thus, thediffraction efficiency of first-order diffraction light can be expressedas: ##EQU3##

Subsequently, the shape shown in FIG. 2B where a<0 may be expressedsimilarly as above, in terms of a phase function, and a result such asshown in FIG. 7 may be provided. With regard to this phase distribution,diffraction efficiency of first-order diffraction light may becalculated, as follows: First, ##EQU4## is given, and it follows fromthis that ##EQU5## Comparing equations (3) and (4) with each other whiletaking note of the sign of "a", it is seen that they can be synthesizedinto ##EQU6## This equation is totally symmetrical with respect to thepositiveness/negativeness of the parameter "a". If b=0 in equation (5),it follows that

    |C.sub.1 |.sup.2 =(8/π.sup.2)[1-sin{π(|a|/2)}]

This is exactly as described with reference to equation (1).

FIG. 8 shows the result of calculation of diffraction efficiency offirst-order diffraction light, while taking the parameter b,representing the second time etching depth d₂, on the axis of abscissa.The magnitude of |a| which represents the alignment error, changes in arange from 0 to 0.4.

It is seen from this graph that, in a case of zero alignment error(|a|=0), a maximum diffraction efficiency is attainable with b=0. Inother words, the diffraction efficiency becomes highest when

    d.sub.2 =λ/[4(n-1)]

is satisfied.

As compared therewith, if the alignment error is not zero (|a|≠0), thevalue of b with which the diffraction efficiency becomes largest shiftsfrom the position b=0, in the direction of b<0. Also, it is seen thatthis position is changeable with the magnitude of the alignment error.Namely, assuming the presence of an alignment error of a certainmagnitude, the etching depth with which a maximum diffraction efficiencyis attainable can be determined fixedly.

More specifically, if for example there is an alignment errorcorresponding to |a|=0.1, a highest diffraction efficiency may beprovided when the etching depth d₂ in the second etching processcorresponds to b=-0.15, that is, the amount smaller by about 15% thanthe value as determined by

    d.sub.2 =λ/[4(n-1)]

Thus, in this embodiment, the magnitude of alignment error is measuredand, in accordance with it, the etching depth d₂ of the second etchingis controlled. By this, the effect of alignment error on the diffractionefficiency can be reduced.

On the basis of this, the present invention enables manufacture of gooddiffractive optical elements.

Next, the manner of measuring the alignment error will be described.FIGS. 9A and 9B are schematic views of a first mask 102 and a secondmask 105, respectively. If a positive type resist is used, images ofopenings 10 and 11 will be transferred to a glass substrate. These masksare formed with pattern groups 12 and 13 to be used for forming a binarytype diffractive optical element. Additionally, there are alignmenterror measurement marks 14 and 15, formed on the first and second masks102 and 105, respectively.

The pattern group 12, the alignment error measurement mark 14, thepattern group 13, and the alignment error measurement mark 15 aredisposed in a predetermined positional relationship, such that, onlywhen the pattern groups 12 and 13 are registered idealistically witheach other upon the glass substrate, the images of the two alignmenterror measurement marks 14 and 15 are placed exactly at the sameposition.

FIG. 10 shows an example of positional relation between an image 20 ofthe alignment error measurement mark 14 and an image 21 of the alignmenterror measurement mark 15, after completion of second exposure (processF).

The two masks 102 and 105 shown in FIGS. 9A and 9B are equipped withalignment marks (not shown), and the positional relation between thesemasks is controlled by using these alignment marks. Practically,however, due to various factors, pattern transfer is performed withmisalignment. FIG. 10 shows an example with such misalignment.

Here, by measuring the positional relation between the images 20 and 21of the two alignment error measurement marks 14 and 15, the positionalrelation between the images of the pattern groups 12 and 13 can bedetected. The deviation between the images 20 and 21 may be resolvedinto x-component and y-component. Of these components, x-component (Δx)corresponds to the alignment error which adversely affects thediffraction efficiency, in this example.

In this embodiment, to a measured alignment error Δx, an optimum etchingdepth d₂ in the second etching process (process G) is calculated inaccordance with equation (5), and the second etching process isperformed on the basis of this information. By this, the effect ofalignment error on the decrease of diffraction efficiency can beminimized.

While the embodiment has been described with reference to an examplewhere four-level binary structure is manufactured by use of two masks,the procedure is similarly applicable to manufacture of binary typediffractive optical element with more levels (steps).

Also, while the foregoing description has been made to an example ofbinary type diffractive optical element wherein patterns of the sameperiod are repeated one-dimensionally, the present invention issimilarly applicable to a binary diffractive optical element of the typehaving a two-dimensional period distribution and, additionally, havingnon-uniform period, such as a Fresnel lens, for example. In that case,as regards the alignment error for calculation of etching depth, notonly, Δx in FIG. 10 but also Δy may be used.

Next, an embodiment of illumination system and projection exposureapparatus for manufacture of semiconductor devices, in which a binarydiffractive optical element having been manufactured in accordance withthe present invention is incorporated as a lens element of lightcollecting or diverging system, will be explained.

FIGS. 11A and 11B are schematic views of a main portion of anillumination system having a diffractive optical element, according toan embodiment of the present invention. FIG. 11A is taken on a firstplane, i.e., X-Z plane. FIG. 11B is taken on a second plane, i.e., Y-Zplane.

Denoted in the drawings at 1 is a light source such as a Hg lamp orexcimer laser, for example. Denoted at 2 is a beam shaping opticalsystem including a beam compressor, for example. It serves to adjust thelight from the light source 1 into a desired beam shape, and to projectthe same on the light entrance surface 5a of an optical integrator 5which serves as a homogenizer. As will be described later, the opticalintegrator 5 has two diffractive optical elements, that is, first andsecond diffractive optical elements having different refractive powerswith respect to both of X-Z sectional plane (FIG. 11A) and Y-Z sectionalplane (FIG. 11B). A plurality of secondary light sources are defined atthe light exit surface 5b thereof. Denoted at 3 is a condenser lens forcollecting light beams from the secondary light sources, at the lightexit surface of the optical integrator 5, so that they are superposedone upon another on the surface 4 to be illuminated.

In the illumination system according to this embodiment, the lightemitted by the light source 1 is transformed by the beam shaping opticalsystem 2 into a desired beam diameter, and then it is projected on thelight entrance surface 5a of the optical integrator 5. In response, aplurality of secondary light sources are defined at the light exitsurface 5b. The lights from these secondary light sources at the lightexit surface 5b are then projected by the condenser lens 3 toKoehler-illuminate the surface 4 to be illuminated. Here, the opticalintegrator 5 is arranged to have a numerical aperture θx with respect toX-direction sectional plane of FIG. 11A and a numerical aperture θy withrespect to Y-direction sectional plane of FIG. 11B, which are differentfrom each other, such that the illumination regions along thesesectional planes have different widths Dx and Dy.

FIGS. 12A and 12C and FIGS. 12B and 12D are schematic views of a mainportion of the optical integrator 5, shown in FIGS. 11A and 11B. FIGS.12A and 12C are on the X-Z plane, while FIGS. 12B and 12D are taken onthe Y-Z plane.

As shown in FIGS. 12A and 12C and FIGS. 12B and 12D, the opticalintegrator 5 comprises a number of small diffractive optical elements21, shown in detail in FIG. 12C, with focal length f_(ix), having apower in the X-direction sectional plane as viewed in the drawing andbeing arrayed at the front side (light source 1 side) of the samesubstrate 20. Also, the optical integrator further comprises a number ofsmall diffractive optical elements 22, shown in detail in FIG. 12D, withfocal length f_(iy), having a power in the Y-direction sectional planeas viewed in the drawing and being arrayed at the back side of thesubstrate. The combinations of these small diffractive optical elements21 and 22 provide a first diffractive optical element and a seconddiffractive optical element, respectively. As regards the focal lengthsf_(ix) and f_(iy), they are in a relation f_(ix) >f_(iy) and both ofthem have a positive value.

As shown in FIGS. 12A and 12C and FIGS. 12B and 12D, the refractivepowers of the first and second diffractive optical elements 21 and 22 aswell as the thickness of the substrate 20 and the refractivity of thematerial thereof, for example, are selected and adjusted so that thefocal point position of the light passing through the first and seconddiffractive optical elements 21 and 22 is in exact registration, withrespect to the first and second planes. With this arrangement, anillumination region of predetermined shape can be defined efficiently.

Small diffractive optical element of this embodiment can be manufacturedby use of optical lithography technique as described. Thus, an elementlens smaller than an element lens as attainable with conventionalpolishing process, for example, can be manufactured easily. This makesit possible to increase the number of element lenses considerably andconsequently to increase the number of secondary light sourcesconsiderably. Thus, illumination of higher uniformity can be realized.

FIG. 13 is a schematic view of a main portion of a projection exposureapparatus having a diffractive optical element, according to anembodiment of the present invention. Denoted in the drawing at 1 is alight source, and denoted at 2 is a beam shaping optical system. Denotedat 5 is an optical integrator, and denoted at 3 is a condenser lens.These components are similar to those used in the illumination system ofFIGS. 11A and 11B.

Denoted at 51 is a stop, which corresponds to the position of thesurface 4 to be illuminated (FIGS. 11A or 11B). Denoted at 51 is a stopimaging lens for projecting an image of the aperture shape of the stop51 on to a reticle 50 which is disposed on the surface to beilluminated. The illumination region on the reticle 50 surface has ashape analogous to the aperture shape of the stop 51. Denoted at 54 is aprojection lens (projection optical system) for projecting a pattern onthe reticle 50 surface on to the surface of a photosensitive substrate(wafer) 56. Denoted at 53 is driving means for moving the reticle 50,and denoted at 55 is driving means for moving the wafer 56.

In this embodiment, a circuit pattern of the reticle 50 is printed, byprojection through the projection lens 54, on the wafer 56 being coatedwith a photosensitive material such as a resist, in step-and-scanprocedure. In an exposure apparatus of step-and-scan method, the patternof the reticle 50 is not illuminated at once. Rather, the illuminationarea is defined in a slit-like shapes for example. Thus, a pattern ofthe reticle 50 placed within such illumination area is projected andtransferred by the projection lens 54 to the exposure area on the wafer56.

The reticle 56 is placed on a reticle stage, and it can be scanninglymoved in X direction, for example, by the driving means 53. The wafer 56is placed on a movable stage which can be scanningly moved by thedriving means 55, along the X-axis direction and in an oppositedirection to the reticle 50 movement. More specifically, the reticle 50and the wafer 56 are scanningly moved in opposite directions, insynchronism with each other, at a speed ratio corresponding to theprojection magnification of the projection lens 54.

While in this embodiment a diffractive optical element is used in anillumination system, a diffractive optical element of ring-like shapemanufactured in accordance with the present invention may be used in aprojection optical system.

Next, an embodiment of device manufacturing method which uses aprojection exposure apparatus such as described above, will beexplained.

FIG. 14 is a flow chart of procedure for manufacture of microdevicessuch as semiconductor chips (e.g. ICs or LSIs), liquid crystal panels,or CCDs, for example.

Step 1 is a design process for designing a circuit of a semiconductordevice. Step 2 is a process for making a mask on the basis of thecircuit pattern design. Step 3 is a process for preparing a wafer byusing a material such as silicon. Step 4 is a wafer process which iscalled a pre-process wherein, by using the so prepared mask and wafer,circuits are practically formed on the wafer through lithography.

Step 5 subsequent to this is an assembling step which is called apost-process wherein the wafer having been processed by step 4 is formedinto semiconductor chips. This step includes assembling (dicing andbonding) process and packaging (chip sealing) process. Step 6 is aninspection step wherein operation check, durability check and so on forthe semiconductor devices provided by step 5, are carried out. Withthese processes, semiconductor devices are completed and they areshipped (step 7).

FIG. 15 is a flow chart showing details of the wafer process. Step 11 isan oxidation process for oxidizing the surface of a wafer. Step 12 is aCVD process for forming an insulating film on the wafer surface.

Step 13 is an electrode forming process for forming electrodes upon thewafer by vapor deposition. Step 14 is an ion implanting process forimplanting ions to the wafer. Step 15 is a resist process for applying aresist (photosensitive material) to the wafer. Step 16 is an exposureprocess for printing, by exposure, the circuit pattern of the mask onthe wafer through the exposure apparatus described above.

Step 17 is a developing process for developing the exposed wafer. Step18 is an etching process for removing portions other than the developedresist image. Step 19 is a resist separation process for separating theresist material remaining on the wafer after being subjected to theetching process. By repeating these processes, circuit patterns aresuperposedly formed on the wafer.

With these processes, high density microdevices can be manufacturedeasily.

Next, an embodiment of manufacturing system with which a manufacturingmethod of the present invention can be embodied, will be explained withreference to FIG. 16.

In FIG. 16, denoted at 201 is an exposure apparatus for performing anexposure process. Denoted at 202 is a coater and developer, forperforming resist coating and resist development after exposure. Denotedat 203 is an etcher for performing the etching process while using adeveloped resist pattern as a mask pattern. Denoted at 204 is alignmenterror measuring means for measuring, after second time resist patterndevelopment, alignment error between a mask having been used previouslyand a mask just to be used or just having been used. The optical elementmanufacturing method such as described with reference to FIGS. 4 or 5,for example, can be embodied in this manufacturing system, for example.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. A diffractive optical element manufacturingmethod, comprising:a first process for forming a mask pattern using aresist material on a substrate; and a second process for etching astep-like structure on the substrate by use of the mask pattern, whereinthe first and second processes are repeated N times, wherein an non-zeroalignment error is generated between the mask pattern as formed throughthe (k)th time first process and the mask pattern as formed through the(k-1)th time first process where 2≦k≦N, wherein, before execution of the(k)th time second process, there is a process for determining thenon-zero alignment error between the mask pattern as formed through the(k)th time first process and the mask pattern as formed through the(k-1)th time first process, and wherein a depth of the step-likestructure effected by the (k)th time second process is determined inaccordance with the determined non-zero alignment error.
 2. A methodaccording to claim 1, wherein the first and second processes arerepeated by N times, by which a step-like structure with 2^(N) levels isformed on the substrate.
 3. A method according to claim 1, wherein themask pattern comprises a resist having been developed.
 4. A methodaccording to claim 3, wherein the first process includes a sub-processfor coating the substrate with a resist, a sub-process forlithographically transferring a pattern on to the substrate, and asub-process for developing the pattern transferred to the substrate. 5.A method according to claim 3, wherein the second process includes asub-process for etching the substrate, wherein the depth of thestep-like structure as determined in accordance with the determinednon-zero alignment error corresponds to the depth of the etching, and asub-process for removing a resist from the substrate.
 6. A diffractiveoptical element manufacturing method, comprising:a first process forforming a mask pattern using a resist material on a substrate; a secondprocess for etching a step-like structure on the substrate by use of thefirst mask pattern; a third process for forming a second mask patternusing a resist material on the substrate, wherein an non-zero alignmenterror is generated between the mask pattern and the second mask pattern;a fourth process for determining the non-zero alignment error betweenthe first and second mask patterns; and a fifth process for etching astep-like structure on the substrate by use of the second mask pattern,wherein a depth of the step-like structure effected by said fifthprocess is determined in accordance with the determined alignment error.7. A diffractive optical element manufacturing method, comprising:afirst process for forming a mask pattern using a resist material on asubstrate; a second process for, an non-zero alignment error having beengenerated between a mask pattern just having been formed and a maskpattern previously formed, determining the non-zero alignment errorbetween the mask pattern just having been formed and the mask patternpreviously formed; and a third process for etching a step-like structureon the substrate by use of the mask pattern just having been formed,wherein a depth of the step-like structure effected by said thirdprocess is determined in accordance with the determined non-zeroalignment error.
 8. A diffractive optical element manufacturing method,comprising:a first process for forming a mask pattern using a resistmaterial on a substrate; and a second process for depositing a step-likestructure on the substrate by use of the mask pattern, wherein the firstand second processes are repeated N times, wherein an non-zero alignmenterror is generated between the mask pattern as formed through the (k)thtime first process and the mask pattern as formed through the (k-1)thtime first process where 2≦k≦N, wherein, before execution of the (k)thtime second process, there is a process for determining the non-zeroalignment error between a mask pattern as formed through the (k)th timefirst process and a mask pattern as formed through the (k-1)th timefirst process, and wherein a height of the step-like structure effectedby the (k)th time second process is determined in accordance with thedetermined non-zero alignment error.
 9. A diffractive optical elementmanufacturing method, comprising:a first process for forming a maskpattern using a resist material on a substrate; a second process fordepositing a step-like structure on the substrate by use of the firstmask pattern; a third process for forming a second mask pattern using aresist material on the substrate, wherein an non-zero alignment error isgenerated between the mask pattern and the second mask pattern; a fourthprocess for determining the non-zero alignment error between the firstand second mask patterns; and a fifth process for depositing a step-likestructure on the substrate by use of the second mask pattern, wherein aheight of the step-like structure effected by said fifth process isdetermined in accordance with the determined non-zero alignment error.10. A diffractive optical element manufacturing method, comprising:afirst process for forming a mask pattern using a resist material on asubstrate; a second process for, an non-zero alignment error having beengenerated between a mask pattern just having been formed and a maskpattern previously formed, determining the non-zero alignment errorbetween the mask pattern just having been formed and the mask patternpreviously formed; and a third process for depositing a step-likestructure on the substrate by use of the mask pattern just having beenformed, wherein a height of the step-like structure effected by saidthird process is determined in accordance with the determined non-zeroalignment error.
 11. A method comprising:providing a first mask; usingthe first mask to form a step-like structure on a substrate; providing asecond mask, wherein an non-zero alignment error is generated betweenpositioning of the first mask and the second mask; determining thenon-zero alignment error between positioning of the first mask and thesecond mask; and using the second mask to form a step-like structure ona substrate, wherein the height or depth of the step-like structureeffected by using the second mask is set in accordance with the non-zeroalignment error determined in said determining step.